The present invention relates to a method and apparatus for synchronizing an MDPS (Motor Driven Power Steering) motor and a motor position sensor, and more particularly, to a method and apparatus for synchronizing a rotational position of a rotor of an MDPS motor with a motor position sensor.
In general, the position of a three-phase brushless motor of a MDPS system must be accurately calculated in order to control the motor.
A stator of the three-phase brushless motor typically includes field poles and a frame, and the field poles are fixed to the frame through screws or bolts. Furthermore, a rotor of the three-phase brushless motor includes a permanent magnet in which N and S poles are repetitively formed.
For rotation of the rotor of the motor, rotating fields need to be successively formed. In order to form such successive rotating fields, a current applied to a three-phase coil disposed at a stator winding needs to be commutated at an appropriate time. For such commutation at an appropriate time, the position of the rotor must be accurately recognized. The commutation refers to an operation of changing the current direction of the motor stator coil such that the rotor can be rotated. For a smooth operation of the motor, the position of the rotor must be accurately matched with a commutation point of a phase current. Such an operation requires a motor position sensor for detecting the position of the rotor. In general, a hall sensor is used to detect the position of the rotor, the hall sensor having a potential difference that is changed according to a change of magnetic flux.
However, in order to detect the position of the rotor through the motor position sensor such as a hall sensor, a preceding operation is required to synchronize the initial rotational position of the motor with the motor position sensor. According to a conventional synchronization method, a line voltage of a counter electromotive force induced in a stator winding of a motor is measured with the motor rotated by an external force, and compared to an output pulse of the hall sensor, and an offset between a zero crossing point of the line voltage and a switching point of the output pulse of the hall sensor is calculated. Then, the offset is corrected to zero or subtracted from an output of the motor position sensor in a software manner, in order to perform synchronization.
However, since the conventional synchronization method requires a separate driving device for driving the motor and a separate measuring device for measuring the line voltage and the output voltage of the hall sensor, the cost is inevitably increased. Furthermore, an error which occurs during measurement degrades the control performance. Moreover, since an ECU and the motor need to be separated from each other in order to measure the line voltage and the output pulse of the hall sensor, the manufacturing process including separation, measurement and reassembly operations inevitably has inefficiency.